1. Field of the Invention
The present inventions relate to at least one image forming apparatus that forms an image by scanning a photoconductor with a light beam and at least one correction data generation method.
2. Description of the Related Art
In general, an image forming apparatus is known that performs image formation by developing, using toner, an electrostatic latent image formed by scanning a photoconductor with laser light and transferring a toner image formed on the photoconductor to a transfer material. The image forming apparatus corrects (performs shading on) the light intensity of laser light in accordance with an exposure position on the photoconductor. The reason this is performed is to correct nonuniformity in characteristics of sensitivity at a plurality of positions corresponding to laser light on the photoconductor and nonuniformity in light intensity of laser light guided onto the photoconductor by optical characteristics of an optical member such as a lens or a mirror, which guides laser light onto a photoconductor, in a main scanning direction. A main scanning direction is a direction in which laser light scans a photoconductor.
Previously, in correction of light intensity in a main scanning direction, the light intensity of laser light is changed from exposure position to exposure position on a photoconductor in the main scanning direction using a generation time of a BD signal as a reference. In contrast, in correction of light intensity in a rotation direction of the photoconductor (a sub-scanning direction), an exposure position of laser light is determined on the photoconductor in the sub-scanning direction from a photoconductor home position and laser light is changed so as to have a light intensity corresponding to a determination result. An exposure position in the main scanning direction is determined by counting a clock signal output from an oscillator using a BD signal as a reference (for example, see Japanese Patent Application Laid-Open No. 2004-223716).
FIG. 16 illustrates a correction profile 1601, a correction profile 1602, and a correction profile 1603. The correction profile 1601 is a correction profile for correcting nonuniformity in characteristics of sensitivity of a photoconductor. The correction profile 1602 is a correction profile for correcting nonuniformity in light intensity of laser light in the main scanning direction, the laser light having been guided onto the photoconductor by optical characteristics of an optical member. The correction profile 1603 is a correction profile obtained by multiplying the correction profile 1601 by the correction profile 1602. The horizontal axis of FIG. 16 represents a scan position of laser light in the main scanning direction in millimeters, and the vertical axis of FIG. 16 represents a correction amount of the light intensity of laser light in the case where it is assumed that the light intensity of laser light on the photoconductor when the light intensity of laser light is not corrected corresponds to 100%.
For correction of characteristics of sensitivity of the photoconductor, for example, laser-light light intensity correction is needed with a spatial frequency having a period of about 12 mm as a distance on the surface of the photoconductor and with a high resolution greater than or equal to 8 bits (256 levels of gray). In contrast, for correction of optical characteristics of the optical member, for example, light intensity correction is needed with a spatial frequency having a period of about 26 mm as a distance on the surface of the photoconductor and with a high resolution greater than or equal to 8 bits (256 levels of gray).
For pieces of correction data for characteristics of sensitivity and pieces of correction data for optical characteristics of the optical member, pieces of data at positions of plots illustrated in FIG. 16 are stored in a memory unit and pieces of data at positions each of which is between plots are generated by linear interpolation computation. A piece of correction data is read from the memory unit in accordance with an exposure position of laser light, and a piece of light-intensity correction data for laser light is generated by computation in accordance with the read piece of data. That is, previously, a piece of correction data for characteristics of sensitivity of the photoconductor has been read at a period of 12 mm as a spatial frequency, and a piece of correction data for optical characteristics of the optical member has been read at a period of 26 mm as a spatial frequency.
In the case where one main scanning period of laser light is 10 kHz, the scan speed of laser light on the photoconductor is 1000 mm/second. Light intensity correction for laser light in the main scanning direction is performed by converting the correction profile 1603 into an analog signal by a DA converter inside a laser driver and then correcting a driving current to be supplied to a semiconductor laser using the analog signal obtained as a result of the conversion.
However, in the case where a read period of a piece of correction data for characteristics of sensitivity of the photoconductor differs from a read period of a piece of correction data for optical characteristics of the optical member, the relative read timing for pieces of correction data becomes nonperiodic in a one-scan-line period. In the case where relative read timings for pieces of correction data become nonperiodic, there may be the case where the relative read timing for pieces of correction data becomes fast and there may be the case where an electric current correction operation for a correction amount is necessary many times for a short period of time.
For example, an electric current value at a position of 11 mm is a value obtained when the light intensity of laser light corresponds to 88.5% in the main scanning direction in FIG. 16; however, the electric current value needs to be immediately changed to a value obtained when the light intensity of laser light corresponds to 87.5% at a position of 12 mm. In such a case, switching to pieces of correction data for optical characteristics of the optical member to be used for computation needs to be performed since a piece of correction data for optical characteristics of the optical member is read immediately after a piece of correction data for characteristics of sensitivity of the photoconductor is read. An image forming apparatus needs to include a circuit the operation speed of which is fast, in order to do these processes.
For such a high-speed and high-accuracy digital computation circuit operation and an analog operation, a differential circuit or the like needs to be driven at high power and thus heat generated by a driving circuit increases. Thus, there is an issue in that a driving circuit becomes large because of a heat-dissipating component, a power-source stabilizing circuit, and the like and the manufacturing cost is increased because of a large scale of the driving circuit.
The present inventions provide at least one image forming apparatus that reduces an operation speed of a unit that generates pieces of correction data with which the light intensity of laser light is corrected.